1. Field of the Invention
The present invention relates in general to a method for forming a metal nitride film and more particularly to a method for growing metal nitride films such as titaniumnitride (TiN), tungsten nitride (WN) or tantalum nitride (TaN) films suitably used as an electronic conductor film in a semiconductor device and the like.
2. Description of the Related Art
A metal nitride film, a titanium nitride film in particular, is conventionally and widely employed as a contact layer or a diffused barrier layer for an underlying layer on which aluminum wiring, contacts and the like are provided.
As a method for the deposition of such a titanium nitride, a reactive sputtering is widely used wherein titanium is sputtered on a substrate in a nitrogen atmosphere.
However, in order to meet the needs of downsizing and high integration of semiconductor circuits, an increase in an aspect ratio representing a ratio of width to depth of a trench for a contact hole or buried wiring provided on an interlayer dielectric is now required. Since conventional reactive sputtering cannot provide titanium nitride film showing excellent step coverage, the demand for the deposition of the titanium nitride film into a fine contact hole or trench with a high aspect ratio has not yet been met.
A variety of methods of CVD (chemical vapor deposition), instead of a reactive sputtering, are currently utilized as a means to meet the need of providing a fine contact hole or trench for high aspect ratio wiring.
One method of CVD is thermal CVD, wherein titanium tetrachloride (TiCl4) and ammonia (NH3) are heated to a high temperature so that a titanium nitride film is grown on a substrate (xe2x80x9cProperties of LPCVD TiN Barrier Layersxe2x80x9d, J .T. Hillman, D. W. Studiner, M. J. Rice. and C. Arena, Micro-electronic Engineering 19 (1992) PP. 375-378) and another is MOCVD (Metal Organic Chemical Vapor Deposition) wherein tetrakis-dimethylamino-titanium [Ti(N(CH3)2)4] is thermally decomposed so that carbon-containing titanium nitride (TiN:C) film is grown on a substrate (xe2x80x9cEnhanced MOCVD Titanium Nitride Film for Barrier Metal Application in Sub-half Micron Technologyxe2x80x9d, Chin-Kun Wang, Lu-Min Liu, Marvin Liao, Huang-Chung Cheng, and Mou-Shiung Lin. 1995 DRY PROCESS SYMPOSIUM (1995) PP. 129-133).
Others methods include plasma CVD or photo CVD methods for forming a titanium nitride film. In these methods, because a reaction tends to occur easily in the vapor phase; and plasma or light has directivity. Therefore, it is difficult to have a good step coverage. These methods are not suited to forming a titanium nitride film used as a contact layer or a barrier metal layer.
Since the conventional thermal CVD uses titanium tetrachloride (TiCl4) in the process, there is a problem in that chlorine residue remains in the titanium nitride film. In the conventional method, a temperature exceeding 600xc2x0 C. is required to reduce a residual amount of chlorine in the film.
However, because aluminum is melted at a deposition temperature exceeding 550xc2x0 C., such a high temperature CVD is not applicable once the formation of aluminum wiring has been completed.
To further reduce the concentration of residual chlorine in a film, ammonia thermal annealing is generally carried out in the same reactor continuously, following the formation of a titanium nitride film (Japanese Laid-Open Application No. Hei 6-510089). If, however, a temperature for annealing is decreased so as to apply the high temperature CVD method even after the completion of aluminum wiring, it causes an insufficient elimination of chlorine and an unsatisfactory nitridation of the film. Particularly, if the temperature for annealing is less than 550xc2x0 C., the film nitridation is not enough, and when the film is exposed to air, oxygen or water is adsorbed to a site where the bonding of chlorine is broken, causing the oxidation of the titanium nitride film, thus rendering the film useless.
On the other hand, the conventional MOCVD method allows the deposition at a relatively low temperature of about 400xc2x0 C. and is applicable even after the formation of aluminum wiring. However, this method also has disadvantages in that, because it uses tetrakis-dimethylamino-titanium [Ti(N(CH3)2)4] as a processing material, a lot of carbon resides in the titanium nitride film. Due to a high specific resistance of a film, when exposed to air, oxidation occurs easily and the quality of the film is made unusable due to secular change.
The best way to resolve this problem seems to be to carry out the deposition and nitridation using a nitrogen gas plasma little by little. However, if a carbon-containing titanium nitride (TiN:C) film is used as a barrier metal for contact, there is a risk that an underlying transistor is broken due to the collision of the nitrogen gas plasma.
In view of the above, it is an object of the present invention to provide a method for forming a metal nitride film having a low specific resistance as well as an excellent quality, even if it is obtained by the CVD processes carried out at a low temperature, and a method of being able to be applied even after the formation of aluminum wiring.
According to a first aspect of the present invention, there is provided a method of forming a metal nitride film comprising the steps of growing a metal nitride film on the substrate, and carrying out a heat treatment of the metal nitride film, while it is exposed to light, in an atmosphere of gas including a compound or group represented by a chemical formula of NmHn (N is a nitrogen atom, H being a hydrogen atom and, m and n being any natural number).
According to a second aspect of the present invention, there is provided a method of forming a metal nitride film, wherein the above compound or group represented by the chemical formula of NmHn comprises at least one member selected from the group consisting of NH3 and NH, NH2, NH4, and N2H3 and N2H4.
A preferable mode is one that wherein comprises a step of repeating, alternately and a predetermined number of times, a process of growing the metal nitride film on the substrate and a process of thermally treating the metal nitride film while it is exposed to light in the gas atmosphere.
Also, a preferable mode is one that wherein comprises a step of carrying out, in the same reactor, a process of growing the metal nitride film on the substrate and a process of thermally treating the metal nitride film while it is exposed to light in the gas atmosphere.
Also, a preferable mode is one wherein the above metal nitride film formed on the substrate comprises at least one member selected from the group consisting of titanium nitride, carbon-containing titanium nitride, oxygen-containing titanium nitride, tantalum nitride and tungsten nitride.
Also, a preferable mode is one that wherein comprises a step of growing the metal nitride film on the substrate by using CVD (Chemical Vapor Deposition).
Moreover, a preferable mode is one wherein the above light is ultraviolet.